Research on Hepatitis C (HC) has followed several lines. We have cloned and sequenced the entire genome of HC virus (HCV) and expressed the structural genes in a baculovirus expression system and the entire coding region of the genome in recombinant vaccinia virus.Using the expression products we have isolated human monospecific B cell lines expressing antibody to the HCV core and envelope proteins.The human antibodies to the HCV core protein have been mapped to specific epitopes. One of these antibodies reacts to an epitope near the amino terminus that is well known. The other however, recognizes an epitope near the carboxy terminus that has not been described. We are currently evaluating how common antibody to this epitope is among HCV patients. We also have made mouse monoclonal antibodies to the structural genes, but they are not yet characterized. We have diagnostic assays based on the baculovirus expression products and have shown that up to 30% of chronically infected patients have antibody to one of the surface glycoproteins. We are presently developing an anti-HCV core specific for IgM. We hope to use such an assay to distinguish between patients who have recovered from patients who are asymptomatic but chronically infected. Such an assay may also prove useful in following patients on treatment protocols. We have identified and characterized a T-cell epitope in the NS5 (polymerase) region of the polyprotein.Additional T-cell epitopes are being sought by several methods and in several regions of the viral polyprotein including structural and non-structural proteins. In collaboration with C. Rice we have characterized the NS3 protease and determined the processing of the HCV polyprotein. We have a recombinant vaccinia virus containing the entire open reading frame of the HCV genome which we will evaluate in the chimpanzee model as a potential vaccine. We also have several full length cDNA clones that are being evaluated in transfection systems for infectivity. If one of these clones is infectious it will expand enormously our ability to study and manipulate this virus.